From wow.incgamers.com

Threat Level

Insert details of the level of threat Firestones generate.

Facts about Firestones

• Require a Soul Shard to conjure.
• Equipped in the ranged slot, therefore can use weapon and offhand slot at same time.
• The talent Master Conjuror increases spell damage and effect by 15% with 1 point and 30% with 2.
• As a conjured item they will disappear if your character logs out or is disconnected for 15 minutes or more.